Implantable stents are used, for example, for the treatment of stenoses in coronary vessels with the aid of a catheter. Other areas of application of implants of this type are, for example, so-called aneurysm coils.
With implants of this type, the fundamental problem exists after the implantation when the state of the implant must be able to be monitored, in particular, in the chronological behavior after the insertion. For this purpose, the use of imaging methods is known, such as an x-ray examination in which contrast agent must often be injected for better display of the implant. Both the x-ray radiation strain and also the application of the contrast agent represent undesirable strains for the body of the patient. Furthermore, the state of implants, which particularly comprise metal alloys having a predominant proportion of elements of low atomic number (such as magnesium) is hardly detectable fundamentally using angiography.
Various goals are desirable in connection with monitoring the implant. Thus, establishing damage, such as breaking off of struts of the base structure of the implant or recognizing strut cracks, is of interest, in particular, in nondegradable implants.
In degradable implants, the current degradation state of the implant and the time curve of the degradation are important items of information.
Finally, implants having medication depots are also to be cited, in which an important complex of questions comprises whether the deposited medication has already been released and to what degree release of the deposited medication has already occurred.
The examination methods based on x-ray markers and contrast agents referenced hereinabove may only provide little information and, as noted, are stressful to patients.
The fundamental possibility of applying active sensors to the implant, such as a stent, has been discussed in the prior art. However, use of active sensors applied to the implant is not possible, particularly with biodegradable stents, because sensors of this type are based on semiconductor materials which are nondegradable and typically also contain toxic materials, for example, due to the doping of the semiconductor material.